Jun 10 2011:
"The idea that in order to get clear about the meaning of a general term one had to find the common element in all its applications has shackled philosophical investigation."
—The Blue Book, Ludwig Wittgenstein

This question relates to a pretty common mistake that people have been making since at least Aristotle. The problem comes about when you imagine a class of things or ideas and then ask what are the necessary and sufficient conditions for being part of that class. But since Wittgenstein we know better. He pointed out words like "game" which we al know and understand, but nevertheless cannot find a single element or even a set of elements that defines all games and excludes all non-games. He suggested that we think instead in terms of family resemblance. We can all recognize a family resemblance, but it's not normally about one trait. You might have your mom's nose and your sister might have your dad's eyes, etc.

Art is like this—it's a category of things, not a set unified by a single trait or essence. When you start to think about it this way, the problem goes away.

"What is that element that identify a piece of art?" - example. well to others a simple painting can just be a simple painting but to the gifted the same painting can have a million of meaning, it only represents what the viewer can relate.